M42 Tachometer wiring help

[jaredmac11]

Im trying to make sense of the tachometer signal for my E21 M42 swap. I thought this was handled with pin 9 on the C101 but I am not certain.

The ETM makes zero sense for the tachometer, but perhaps it carries another name in the diagram?

Hoping someone is familiar with the ETM and has gone down this path already...

[vpilarrt]

While the engine speed signal does go through pin 9 on C101 there's a lot more to it. The ECU receives a signal from the engine speed sensor (located on the bottom of the engine adjacent to the toothed ring on the front of the crankshaft) where it "processes" it and sends it to the service interval board in the cluster (pin 7 of C1). After more "processing" the now 4 "signal" lines connect to the tach through pins 1, 2, 3 and 4 of C4. I believe the engine code module also "processes" the signal. Use the '92 318ic ETM (its the most complete), see pages 1360-5, 6210-2 and 6210-3.

[jaredmac11]

Ah-ha.. unfortunately I was using the 92 318ic and looking at that same section; it was just all compacted and difficult to tell what was where. This is helpful though, I think I need to look at connecting to the ECU pin and not the C101.

I'll have to confirm. Thanks again, that was very helpful